The present invention is directed to a flexible coupling which has zero backlash in torsion or rotation and also has zero axial backlash. The coupling is particularly useful for connecting a gravure printing cylinder to the main drive box of the printing unit and enables controlling side register of the cylinder by axially shifting the drive shaft.
In a rotogravure press, an engraved cylinder, which has tiny cells for receiving and holding ink, transfers the ink to a sheet or web of material which is pressed onto the engraved cylinder by an impression roller. To provide different colors the press has a series of printing units each containing a cylinder and impression roller and associated parts such as an ink applicator and a doctor blade for removing excess ink. An example of such a gravure press is disclosed in U.S. Pat. No. 2,630,065.
Very often the engraved copy is not always perfectly aligned to the axis of the printing cylinder. Thus, under normal conditions this misalignment of the engraved copy would cause the printed copy for the color of that cylinder to be out of square with the other colors making good register impossible. To compensate for this, the gravure printing cylinder, the ink applicator, and the doctor blades are all mounted in a carriage, which is movable in the frame of the device, and the carriage can be tilted or pivoted around a point which is on the centerline or axis of the drive shaft for the cylinder. The pivoting is accomplished by use of a cam arrangement. By adjusting the cam arrangement, the axis of the gravure printing cylinder can be pivoted relative to the drive shaft axis. With such a pivoting, a coupling, which allows angular misalignment between the axis of the drive shaft of the gear box and the axis of the printing cylinder, is necessary. One type of coupling is known as a Thomas coupling and comprises a pair of hubs with a pack of flexible metal plates positioned between the faces of the hubs and attached to both hubs by spaced bolts so that an angular misalignment between a drive shaft and a driven shaft can be compensated for with a zero backlash in torsion or rotation. However, the coupling does have considerable axial backlash.
In addition to obtaining register due to changing the axis of the printing cylinder relative to the drive shaft, it is also necessary to obtain side printing register which is along the direction of the axis of the cylinder. At present, this is obtained manually by an arrangement or means which shifts the carriage of the printing cylinder relative to the frame of the printing unit to obtain the desired position of the printing cylinder in the frame.